(1) Field of the Invention
The present invention relates generally to a continuous medium printing apparatus, and more particularly to a continuous medium printing apparatus suitable for use as a printer that performs printing on both sides of continuous paper formed at predetermined intervals with perforations by an electrophotographic method.
(2) Description of the Related Art
In continuous paper (continuous medium) on which printing is performed by a continuous medium printing apparatus, there is one in roll form and one folded and stacked at predetermined intervals. Furthermore, in some continuous paper, a plurality of perforations are formed in parallel with the lateral direction of the continuous paper at regular intervals depending on paper size. The continuous paper with perforations can easily be stacked by alternately folding it into mountains and valleys at the perforations or can easily be cut at the perforations.
A conventional continuous medium printing apparatus, which performs printing on both sides of such continuous paper by an electrophotographic method, attaches, for example, continuous paper folded and stacked alternately into mountains and valleys at perforations to a paper hopper. This continuous paper is conveyed while it is being stretched successively by a conveyance system. In an image forming process section, toner images are formed on the obverse and reverse sides of the continuous paper by image forming drums, respectively. Furthermore, the toner images formed on both sides of the continuous paper are fixed by image fixing sections, respectively. In this manner, duplex printing is performed on the continuous paper.
FIG. 13 shows the stretched continuous paper 1. If the continuous paper 1, folded and stacked alternately into mountains and valleys at perforations 1a, is stretched in order to perform printing, mountains and valleys with perforations 1a as apices will be produced in the continuous paper 1, as shown in FIG. 13.
Because of the mountains and valleys with perforations 1a as apices, in the image forming process section, a space will arise between the image forming drum, which transfers a toner image to the continuous paper 1, and the continuous paper 1 and therefore a print trouble area will arise near the perforations 1a. 
There are cases where when printing is performed on continuous paper, an identification mark or the like is printed near the perforations 1a. In such a case, it is desirable to make such a print trouble area as small as possible.
Hence, in the continuous medium printing apparatus, the conveyance system is provided with a scuff section, which is constituted by a scuff roller and a pinch roller disposed opposite to each other at a downstream position of the conveying path of the continuous paper 1 from the image forming process section and the image fixing section. In this scuff section, the continuous paper 1 is conveyed by freely sliding and rotating the scuff roller in the conveying direction of the continuous paper 1, with the continuous paper 1 clamped between the scuff roller and the pinch roller. That is, the continuous paper 1 is stretched by the scuff force (feed force) produced by the scuff roller in the scuff section, and the tension produced in the continuous paper 1 makes the mountains and valleys (unevenness) at the perforations 1a smaller, thereby stabilizing the behavior of the continuous paper 1 in the image forming process section.
Note that the difference d (see FIG. 13) between the mountain and the valley at the perforations 1a in the above-mentioned continuous paper 1 varies depending on the kind of the continuous paper 1, that is, paper basis weight (paper thickness), paper stem, paper size and the like. As shown in FIG. 13, the difference d between the mountain and the valley is defined, for example, as a distance measured in the direction perpendicular to the paper conveying direction.
However, there are cases where the conventional continuous medium printing apparatus cannot cope with various kinds of continuous paper, because of scuff force produced by the scuff section is constant. For instance, in changing the kind of the continuous paper 1, if scuff force is too strong, paper tear will occur at the perforations 1a or there is a possibility that the feed holes formed at regular intervals in the continuous paper 1 will crumble. If, on the other hand, scuff force is insufficient, the continuous paper 1 cannot be sufficiently tensioned, and consequently, there is also a possibility that printing quality will be degraded.
There is also a continuous medium printing apparatus provided along the conveying path of the continuous paper with a plurality of image forming drums for forming images on the continuous paper. In such a continuous medium printing apparatus, however, it is difficult to stretch the continuous paper 1 in each of a plurality of image forming process sections, by the feed force produced by the scuff section disposed at a downstream position of the conveying path of the continuous paper 1 from the image forming process section. Particularly, in the image forming drum disposed at a position away from the scuff section along the conveying path of the continuous paper 1, there is also a problem that print trouble will easily occur near the perforations 1a. 
In addition, in the continuous medium printing apparatus which performs printing on both sides of the continuous paper 1, unevenness near the perforations la in the continuous paper 1 cannot be effectively removed by the feed force produced by the scuff section, because a guide member, a roller and the like, which apply tension to the continuous paper 1 in contact with the opposite side of the continuous paper 1 from the image forming drum, cannot be provided near the image forming process section in order to protect the unfixed toner images formed on both sides of the continuous paper 1.
Furthermore, in the scuff section, the continuous paper 1 is conveyed with the frictional force produced between the outer circumferential surface of the scuff roller and the continuous paper 1, but there are cases where the coefficient of surface friction of the continuous paper 1 is reduced due to matter such as ink or dust on the continuous paper land the like. As a result, there is also a fear that because of the reduction in the coefficient of friction, (1) the feed force produced by the scuff section will be reduced, (2) the continuous paper 1 will slacken because it cannot be stretched, and (3) the contact of the continuous paper 1 with the guide surface or the glass surface of the fixer in the conveying path will damage a formed printed image and reduce printing quality or will damage the guide surface or the fixer.
Incidentally, in order to prevent the occurrence of print trouble near the perforations 1a in the continuous paper 1, a method is known which stabilizes the behavior of the continuous paper 1 in the image forming drum, by disposing tractors for paper conveyance (tractor mechanisms), respectively, at upstream and downstream positions of the conveying path of the continuous paper 1 from the image forming drum and by conveying the continuous paper 1 with the feed pins of the tractor mechanisms fitted into feed holes formed at regular intervals in the laterally opposite portions of the continuous paper 1.
Such a method, however, requires a large space for installing the tractor mechanisms. Therefore, in a continuous medium printing apparatus provided within the same case with a plurality of image forming drums, like a duplex printing apparatus which performs printing on both sides of the continuous paper 1 by an image forming drum for the obverse side and an image forming drum for the reverse side, the tractor mechanisms have to be disposed between these image forming drums in the paper conveying path, and consequently, there is a problem that the size of the apparatus cannot be reduced.
In addition, in the method of disposing tractor mechanisms, respectively, at upstream and downstream positions of the conveying path of the continuous paper 1 from the image forming drum, there is also a problem that when printing is performed on pinless continuous paper having no feed holes, the behavior of the continuous paper in the image forming drum cannot be stabilized.
Furthermore, in order to prevent the occurrence of print trouble near the perforations 1a in the continuous paper 1, a method of varying transfer voltage at an area near the perforations 1a is disclosed in Japanese Laid-Open Patent Publication No. HER 7-261575. Also, a method of applying an electric potential of the opposite polarity from the surface potential of the image forming drum or the like to the continuous paper 1 is disclosed in Japanese Laid-Open Patent Publication No. HEI 5-303287. Furthermore, a method of applying pressure to the continuous paper 1 prior to the transfer of an image in the image forming process section is disclosed in Japanese Laid-Open Patent Publication No. HEI 7-261576. These methods, however, cannot remove unevenness near to the perforations 1a in the continuous paper 1 or the deflection of the continuous paper 1.
The present invention has been made in view of the aforementioned problems. Accordingly, it is an object of the present invention to provide a continuous medium printing apparatus which is capable of preventing the occurrence of print trouble in the vicinity of the perforations in the continuous medium by stabilizing the behavior of the continuous medium in the printing section.
To achieve the above object, the continuous medium printing apparatus of the present invention, which performs printing on both sides of a continuous medium, comprises a conveyance system, a printing section, a feed-force adjustment section, and a feed-force control section. The conveyance system conveys the continuous medium along a conveying path. The printing section performs printing on the continuous medium being conveyed along the conveying path. The feed-force adjustment section adjusts feed force to be applied to the continuous medium, the feed-force adjustment section being disposed on a downstream side of the conveying path from the printing section. The feed-force control section controls the feed-force adjustment section so that the feed force to be applied to the continuous medium varies according to a printing condition.
Therefore, because the feed-force control section of the continuous medium printing apparatus of the present invention controls the feed-force adjustment section so that the feed force to be applied to the continuous medium varies according to a printing condition, the continuous medium can be conveyed with an optimum feed force in accordance with the printing condition. With this, even when duplex printing is performed on a continuous medium under a different printing condition, there is no possibility that the tear or slack of the continuous medium or the like will occur and therefore there is an advantage that can enhance printing quality.
The conveyance system may have a pair of conveyor rollers disposed on a downstream side of the conveying path from the printing section so that they are opposite to each other with the continuous medium therebetween, feed force being applied to the continuous medium by rotating the pair of conveyor rollers with the continuous medium clamped therebetween. Also, the feed-force adjustment section may vary the feed force by adjusting pressure of the pair of conveyor rollers with respect to the continuous medium.
The pair of conveyor rollers may be constituted by a scuff roller which conveys the continuous medium in sliding contact with the continuous medium and a pinch roller which clamps the continuous medium in cooperation with the scuff roller, and the feed-force adjustment section may vary the feed force by adjusting pressure of the pinch roller with respect to the scuff roller so that scuff pressure of the scuff roller with respect to the continuous medium is adjusted.
In addition, the conveyance system may have a pair of conveyor rollers disposed on a downstream side of the conveying path from the deflection quantity detection section so that they are opposite to each other with the continuous medium therebetween, feed force being applied to the continuous medium by rotating the pair of conveyor rollers with the continuous medium clamped therebetween, and the feed-force adjustment section varies the feed force by adjusting pressure of the pair of conveyor rollers with respect to the continuous medium.
At this time, the pair of conveyor rollers may be constituted by a scuff roller which conveys the continuous medium in sliding contact with the continuous medium and a pinch roller which clamps the continuous medium in cooperation with the scuff roller, and the feed-force adjustment section may vary the feed force by adjusting pressure of the pinch roller with respect to the scuff roller so that scuff pressure of the scuff roller with respect to the continuous medium is adjusted.
With these arrangements, the construction of the feed-force adjustment section can be simplified and therefore the construction of the printing apparatus can be simplified.
The feed-force adjustment section may be constituted by an arm member which freely rotatably supports the pinch roller and is pivotable on an arm shaft disposed in parallel with a rotating shaft of the pinch roller; a lever member which is pivotable on a lever shaft disposed in parallel with the rotating shaft of the pinch roller; an elastic member for applying the pressure to the pinch roller, the elastic member being interposed between the arm member and the lever member; and a drive mechanism which drives the lever member to rotate on the lever shaft in order to adjust the scuff pressure, by adjusting a rotational angle of the lever member.
Also, the feed-force adjustment section may be constituted by a first arm member which freely rotatably supports the pinch roller and is pivotable on an arm shaft disposed in parallel with a rotating shaft of the pinch roller; a first lever member which is pivotable on a lever shaft disposed in parallel with the rotating shaft of the pinch roller; a first elastic member for applying the pressure, the first elastic member being interposed between the first arm member and the first lever member; and a first drive mechanism which drives the first lever member to rotate on the first lever shaft in order to adjust the scuff pressure, by adjusting a rotational angle of the first lever member.
With these arrangements, the construction of the feed-force adjustment section can be simplified and therefore the construction of the printing apparatus can be simplified.
Note that the printing condition may be a condition including characteristics of the continuous medium. With this, even when duplex printing is performed on a continuous medium having a different printing condition, there is no possibility that the tear or slack of the continuous medium or the like w ill occur and therefore there is an advantage that can enhance printing quality.
In addition, the printing condition may be a print area rate in the continuous medium. Therefore, even when printing is performed up to the vicinity of the perforations formed in the continuous medium, a print trouble area near the perforations can be reduced and therefore there is an advantage that can enhance printing quality.
Furthermore, the printing condition may be the time that the scuff roller has been used. With this, for instance, even when the scuff roller is worn away because of its use, the continuous medium can be conveyed with an optimum feed force in accordance with the printing condition. As a result, there is no possibility that the tear or slack of the continuous medium or the like will occur and there is an advantage that can enhance printing quality.
The aforementioned object of the present invention can also be achieved by a continuous medium printing apparatus for performing printing on both sides of a continuous medium, comprising: a plurality of endless photosensitive bodies for forming images on the continuous medium, the plurality of endless photosensitive bodies being disposed along a conveying path of the continuous medium; and a rotation control section for controlling the plurality of endless photosensitive bodies so that a circumferential velocity of a downstream endless photosensitive body of the plurality of endless photosensitive bodies becomes faster than that of an upstream endless photosensitive body of the plurality of endless photosensitive bodies.
In the continuous medium printing apparatus, therefore, the tension in the continuous medium on the upstream endless photosensitive body can be held so that the perforations in the continuous medium can be stretched. As a result, a print trouble area near the perforations in the continuous medium can be reduced and there is an advantage that can enhance printing quality.
Note that a circumferential velocity of the upstream endless photosensitive body is faster than that of the downstream endless photosensitive body. With this, a print trouble area near the perforations in the continuous medium can be reduced and therefore there is an advantage that can enhance printing quality.
Furthermore, the aforementioned object can be achieved by a continuous medium printing apparatus for performing printing on both sides of a continuous medium, comprising: a plurality of endless photosensitive bodies for forming images on the continuous medium, the plurality of endless photosensitive bodies being disposed along a conveying path of the continuous medium; and an electric potential control section for controlling electric potential of the plurality of endless photosensitive bodies or electric potential of the continuous medium so that an electrostatic adsorption force of the continuous medium with respect to a downstream endless photosensitive body of the plurality of endless photosensitive bodies becomes greater than that of the continuous medium with respect to an upstream endless photosensitive body of the plurality of endless photosensitive bodies.
In the continuous medium printing apparatus, therefore, the tension in the continuous medium on the upstream endless photosensitive body can be held so that the perforations in the continuous medium can be stretched. As a result, a print trouble area near the perforations in the continuous medium can be reduced and there is an advantage that can enhance printing quality.
Note that the potential control section may make the surface potential of the downstream endless photosensitive body greater than that of the upstream endless photosensitive body. With this, the electrostatic adsorption force of the continuous medium with respect to the downstream endless photosensitive body can be greater than that of the continuous medium with respect to the upstream endless photosensitive body. Therefore, the tension in the continuous medium on the upstream endless photosensitive body can be held with reliability so that the perforations in the continuous medium can be stretched. As a result, a print trouble area near the perforations in the continuous medium can be reduced and there is an advantage that can enhance printing quality.
In addition, the potential control section may make the charged potential of the continuous medium on the downstream drum greater than that of the continuous medium on the upstream drum. Similarly, the electrostatic adsorption force of the continuous medium with respect to the downstream drum can be greater than that of the continuous medium with respect to the upstream drum. Therefore, the tension in the continuous medium on the upstream drum can be held with reliability so that the perforations in the continuous medium can be stretched. As a result, a print trouble area near the perforations in the continuous medium can be reduced and there is an advantage that can enhance printing quality.
Note that the potential control section may vary the electrostatic adsorption force in accordance with a printing condition. With this, the continuous medium can be conveyed with an optimum feed force corresponding to the printing condition. Therefore, even when duplex printing is performed on a continuous medium under a different printing condition, there is no possibility that the tear or slack of the continuous medium or the like will occur and there is an advantage that can enhance printing quality.
Moreover, the aforementioned object of the present invention can be achieved by a continuous medium printing apparatus for performing printing on a continuous medium, comprising: a conveyance system for conveying the continuous medium along a conveying path; a printing section for performing printing on the continuous medium being conveyed along the conveying path; and an automatic feed-force adjustment unit for automatically adjusting feed force to be applied to the continuous medium, the automatic feed-force adjustment unit being disposed along the conveying path. The automatic feed-force adjustment unit includes: a buffer section for sucking up deflection of the continuous medium produced due to a change in the feed force to be applied to the continuous medium, the buffer section being disposed on a downstream side of the conveying path from the printing section; a deflection quantity detection section for detecting a quantity of deflection of the continuous medium sucked up by the buffer section, as a quantity corresponding to the feed force to be applied to the continuous medium; a feed-force adjustment section for adjusting the feed force to be applied to the continuous medium, the feed-force adjustment section being disposed on a downstream side of the conveying path from the deflection quantity detection section; and a feed-force control section for controlling the feed-force adjustment section so that the feed force to be applied to the continuous medium varies according to the deflection quantity detected by the deflection quantity detection section.
Thus, in the continuous medium printing apparatus of the present invention, the automatic feed-force adjustment unit includes the buffer section for sucking up deflection of the continuous medium produced due to a change in the feed force to be applied to the continuous medium, the buffer section being disposed on a downstream side of the conveying path from the printing section. Therefore, the continuous medium has no deflection and can be conveyed stably. The automatic feed-force adjustment unit further includes the deflection quantity detection section for detecting a quantity of deflection of the continuous medium sucked up by the buffer section, as a quantity corresponding to the feed force to be applied to the continuous medium; the feed-force adjustment section for adjusting the feed force to be applied to the continuous medium, the feed-force adjustment section being disposed on a downstream side of the conveying path from the deflection quantity detection section; and the feed-force control section for controlling the feed-force adjustment section so that the feed force to be applied to the continuous medium varies according to the deflection quantity detected by the deflection quantity detection section. Therefore, the tension in the continuous medium can be kept constant and there is an advantage that can enhance printing quality.
Note that the buffer section maybe constituted by a buffer roller resting on one side of the continuous medium so as to be movable radially to absorb possible deflection of the continuous medium and so as to be rollable as a follower on the one side surface of the continuous medium in response to the conveyance of the continuous medium; a pair of driven rollers resting on the another side of the continuous medium so as to be rollable as a follower on the another side surface of the continuous medium in response to the conveyance of the continuous medium; and an urging mechanism for urging the butter roller in the direction of deflection in order to apply buffer pressure to the continuous medium in the direction of deflection. With this, the construction of the buffer section can be simplified and therefore the construction of the printing apparatus can be simplified.
The deflection quantity detection section may detect the position of the buffer roller as the quantity of deflection of the continuous medium. With this, the deflection quantity can be detected reliably and therefore there is an advantage that can enhance printing quality.
The continuous medium printing apparatus of the present invention may further include a buffer-pressure adjustment section for adjusting the buffer pressure which is applied to the continuous medium by the buffer roller. With this, even when the printing condition changes due to an exchange of the continuous medium or the like, buffer pressure can be adjusted so that it becomes optimum with respect to a change in the feed force to be applied to the continuous medium. As a result, the deflection of the continuous medium produced due to a change in the feed force can be reliably sucked up and therefore there is an advantage that can enhance printing quality.
In addition, the buffer-pressure adjustment section may be constituted by a second arm member which freely rotatably supports the buffer roller and is pivotable on a second arm shaft disposed in parallel with a rotating shaft of the buffer roller; a second lever member which is pivotable on a second lever shaft disposed in parallel with the rotating shaft of the buffer roller; a second elastic member for applying the buffer pressure, the second elastic member being interposed between the second arm member and the second lever member; and a second drive mechanism which drives the second lever member to rotate on the second lever shaft in order to adjust the buffer pressure, by adjusting a rotational angle of the second lever member. The second arm member, the second lever member, and the second elastic member may constitute the urging mechanism. With this arrangement, the construction of the buffer-pressure adjustment section can be simplified and therefore the construction of the printing apparatus can be simplified.
Furthermore, the deflection quantity detection section may be constituted by a position detection sensor which detects a position of the second arm member as a position of the buffer roller. With this, the position of the buffer roller can easily be detected and therefore the deflection quantity of the continuous medium can be detected easily and reliably. As a result, there is an advantage that can enhance printing quality and apparatus reliability.
The continuous medium printing apparatus of the present invention may further include a buffer-pressure control section which controls the buffer-pressure adjustment section in order to vary the buffer pressure to be applied to the continuous medium. With this, the buffer pressure to be applied to the continuous medium can be controlled. As a result, there is an advantage that can enhance printing quality and apparatus reliability.
The buffer-pressure control section may control the buffer-pressure adjustment section in accordance with a condition including characteristics of the continuous medium. With this, even when duplex printing is performed on a continuous medium having a different printing condition, the deflection of the continuous medium can be sucked up reliably. As a result, the continuous medium has no deflection and there is an advantage that can stably convey the continuous medium.
In addition, the buffer-pressure control section may control the buffer-pressure adjustment section in accordance with an instruction input from the outside. With this, an optimum buffer pressure corresponding to the continuous medium can be set and the deflection of the continuous medium can be sucked up reliably. As a result, the continuous medium has no deflection and there is an advantage that can stably convey the continuous medium.
The position detection sensor may be constituted by a first position detection sensor which detects that the second arm member has reached an upper limit position corresponding to the case where the deflection quantity of the continuous medium has gone to a predetermined upper value and a second position detection sensor which detects that the second arm member has reached a lower limit position corresponding to the case where the deflection quantity of the continuous medium has gone to a predetermined lower value. The feed-force control section may control the feed-force adjustment section so that the scuff pressure is increased when the first position detection sensor detects the second arm member and is decreased when the second position detection sensor detects the second arm member. With this, the continuous medium can be stretched at all times with a constant tension. As a result, there is no possibility that the tear or slack of the continuous medium or the like will occur and there is an advantage that can enhance printing quality.
The feed-force control section may measure a continuous time period of detecting the second arm member by the first position detection sensor or the second position detection sensor and may give an alarm when the continuous detection time period exceeds a predetermined time period. With this, the feed-force control section can detect the state that the continuous medium cannot be tensioned because of the tear of the continuous medium or the like and the state that the tension in the continuous medium cannot be removed because of the conveyance failure of the continuous medium or the like. As a result, there is an advantage that can enhance apparatus reliability and printing quality.
The continuous medium printing apparatus of the present invention may further include an overrun sensor which detects that the deflection quantity of the continuous medium has gone to an overrun state exceeding an allowable value. The feed-force control section may give an alarm when the overrun sensor detects the overrun state. With this, the feed-force control section can detect the state that the continuous medium cannot be tensioned because of the tear of the continuous medium or the like and the state that the tension in the continuous medium cannot be removed because of the conveyance failure of the continuous medium or the like. As a result, there is an advantage that can enhance apparatus reliability and printing quality.
The overrun sensor may detect the overrun state by the position of the second arm member. The overrun sensor may also detect the overrun state by a rotational angle of the second drive mechanism. With this, the overrun state can be detected with reliability. As result, there is an advantage that can enhance apparatus reliability and printing quality.
The continuous medium printing apparatus of the present invention may further comprise a stopper which regulates rotation of the second arm member when the deflection quantity of the continuous medium exceeds an allowable value. With this, it becomes easy to detect the position of the second arm member. In addition, there is no possibility that the second arm member will interfere with other components because of its excessive rotation and therefore there is an advantage that can enhance apparatus reliability.
The buffer roller may be moved to a position where the buffer roller and the continuous medium do not interfere with each other, when the continuous medium is set into the continuous medium printing apparatus. With this, there is no possibility that when the continuous medium is set into the printing apparatus, the continuous medium will interfere with the buffer roller, and the setting of the continuous paper 1 is easy. As a result, there is an advantage that can quickly set the continuous medium into the continuous medium printing apparatus.
The above and many other objects, features and advantages of the present invention will become manifest to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which preferred embodiments incorporating the principle of the present invention are shown by way of illustrative example.